If only there was a way for your contact list too show you the available apps for each contact... oh wait.
1) My contact list doesn't hot link into an app so I'd have to go to the contacts, look up the person, then look up what messaging service they use, back out and select the app.
2) This assumes the contact list is maintained to have all this info which you're adding another barrier of entry. Even if it was maintained, the app would need the proper support to be hotlinked into it so you're relying on apps to properly support this. Anyone deviates, and well you're fragmented again.
3) Most people I know jump right into the app rather than going through their contacts list. You're talking about a significant change in behavior and muscle memory to socialize with someone.
4) This is all still more friction than someone using iMessage and it just working.
You guys keep suggesting people jump through hoops and barriers when people don't want to and have found a solution where they don't have to.